Facile synthesis of alumina hollow microspheres via trisodium citrate-mediated hydrothermal process and their adsorption performances for p-nitrophenol from aqueous solutions Jiabin Zhou ⇑ , Lei Wang, Zhong Zhang, Jiaguo Yu School of Resources and Environmental Engineering, Wuhan University of Technology, 122 Luoshi Road, Wuhan 430070, PR China State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 122 Luoshi Road, Wuhan 430070, PR China article info Article history: Received 28 September 2012 Accepted 25 November 2012 Available online 5 December 2012 Keywords: Al 2 O 3 microspheres Trisodium citrate Hydrothermal synthesis Adsorption capacity p-Nitrophenol abstract Alumina hollow microspheres with high adsorption affinity toward p-nitrophenol in water were pre- pared by using urea and trisodium citrate as precipitating and mediating agents, respectively, via a sim- ple one-pot hydrothermal synthesis followed by calcination. The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and nitrogen adsorption–desorption isotherms measurement. This study shows that the morphology, specific surface area, and the pore structure of the resulting materials can be controlled by varying the concentration of trisodium citrate. The result of adsorption of p-nitrophenol onto the as- prepared samples revealed that the pseudo-second-order kinetic equation can better describe the adsorption kinetics. Furthermore, adsorption isotherm studies indicated that the resulting alumina microspheres are powerful adsorbents for the removal of p-nitrophenol from water with maximum adsorption capacity of 217.4 mg/g. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Hollow sphere structures have attracted much attention in the general synthesis of functional materials because of their low den- sity, high specific surface area and attractive optical properties, which have been widely used in various fields spanning from arti- ficial cells, energy-storage media, drug-delivery carriers [1–3], and catalysis [4] to nanoscale chemical reactors [5–7]. To date, most of synthetic approaches were essentially focused on various removable templates to obtain these fascinating hollow spherical materials. These templates include spherical silica, car- bon sphere, block copolymer latex, emulsion droplets/micelles [8–11], and gas bubbles [12,13]. However, the introduction of tem- plates into the synthetic routes usually suffers from disadvantages related to high cost and troublesome synthetic procedures, which may prevent them from being used in large-scale applications. As an alternative, template-free approaches based on different mech- anisms were also developed to fabricate hollow spherical materials with desired pore structure and surface properties [14–17]. Among diverse functional materials, hollow boehmite (c-AlOOH) and its oxide derivatives such as c-Al 2 O 3 have been studied intensively over a long period of time because of its broad applications in adsorbents, composite materials, ceramics, cata- lysts, and catalyst supports [18–20]. Aiming at this goal, many kinds of interesting and delicate boehmite nanostructures, such as nanofibers [21], nanobelts [22], nanotubes [23], and bundles of aligned boehmite nanowires [24], as well as flower-like 3D nan- oarchitectures [25] have been prepared. However, it is still a chal- lenge to search for an effective approach to develop aluminum oxides with hierarchically porous nanostructures, which can pro- vide high flow rate during the uptake of pollutants [26–29]. Herein, we present a simple trisodium citrate-assisted hydro- thermal route to prepare Al 2 O 3 hollow microspheres. The effects of trisodium citrate on the morphology and microstructure of the resulting product as well as its formation mechanism were studied. The preliminary adsorption performances of these Al 2 O 3 micro- spheres for removal of p-nitrophenol from water were positive, which makes them promising adsorbent materials for wastewater treatment. 2. Experimental 2.1. Sample preparation All chemicals and reagents used were in analytical grade (Shanghai Chemical Industrial Company) and used without further purification. In a typical synthesis, 3.5 mmol AlNH 4 (SO 4 ) 2 12H 2 O and different amounts of trisodium citrate (0, 0.125, 0.25, 0.5, 0021-9797/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcis.2012.11.050 ⇑ Corresponding author at: School of Resources and Environmental Engineering, Wuhan University of Technology, 122 Luoshi Road, Wuhan 430070, PR China. Fax: +86 27 87885647. E-mail address: jbzhou@whut.edu.cn (J. Zhou). Journal of Colloid and Interface Science 394 (2013) 509–514 Contents lists available at SciVerse ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis